Metal rolling mill motor control



p 1941- T. A. wool; 2,254,338

METAL ROLLING MILL MOTOR CONTROL Filed June 5, 1940 5Hu/vT HELD flUX/L/AIEY HELD CaMPavsn r/Na HELD field winding in series circuit with the motor ture speed changes.

parallel circuit with the Patented Sept. 2,1941

UNITED STATES PATENT 1 OFFICE METAL aormc ifi n ioron common I V Thornton A. Wood, Gary, Ind. 7 Application June 5, 1949, Serial'No. 389,021 I 1 Claim.

This invention is particularly concerned with the regulation of direct current electric motors used to power the working rolls of metal rolling mills.

The problem of regulating these motors has not been adequately solved by prior art arrangements, motor speed variations in the case of strip mills, for instance, being particularly troublesome. One reason for speed regulation difiiculties is that although a direct current motor of the shunt field type is capable of being accurately regulated under many conditions, the rapid speed and load variations encountered in metal rolling mill service cause troubles, and one :1 these arises from motor instability of opera on.

In the interest of providing better speed regu lation, a shunt field motor or the rolling mill type is commonly provided with a compensating armature and which functions to prevent distortion of the field .due to armature reaction. In

' addition to this, an auxiliary field is commonly provided, this being energized by being in shunt circuit with the compensating field winding and intended to prevent unstable motor operation.

The usual arrangement is to provide a rheostat having two banks of resistance, one bank being in series with the energizing circuit of the shunt field of themotor, and the other bank being in series with the auxiliary field circuit, a commonlcontrolling element iunctioning'to add resistance to the shunt field circuit while simultaneously removing resistance from the auxiliary field circuit or vice versa. The rheostat is constructed to perform these two iunctions so that the one iun'ction is entirely dependent on the other, the motor operator having no control whatsoever over the interrelation of the two functions. By correlating the two functions, the auxiliary field current is increasediin proper proportion to decreases in the shunt field current to prevent unstable operation due to arma- Although this prior art arrangement provides control in the case of changes in the armature weed, it does not provide control when the. armature load varies as it does in the case of a metal rolling mill motor. The present invention is intended to provide adequate control when the armature load varies as it does in the case of this type of motor application.

According to the invention, a second rheos'tat is placed in the auxiliary field circuit in bank or resistance provided this circuit by the previously discussed rheostat. This second rheostat is entirely independent oi the other and provides for placing independently variable amounts or resistance parallel that which the. other rheostat variably places in the auxiliary field circuit in accordance withkthe resistance variations in the shunt field circuit.

With such an arrangement load variations on the motor may be compensated by the motor operator, this being impossible in the case or the usual arrangement. That is to say, with the usual arrangement an armature reaction due to a load variation which weakens the shunt field to such an extent that the motor speed increases, is an uncontrollable action, but by the use of the present invention the auxiliary field strength can be increased by thev motoroperator as required to maintain a' constant motor speed, the auxiliary field strength now being variable as required for the purpose whereas it was formerly only variable dependently upon a variation in the field strength during deliberate motor speed changes.

The foregoing is illustrated by the accom- P nyin: diagram.

This diagram shows the exciter energizing the motor shunt field through a circuit I m which variable amounts of the resistance .2 may be '30 placed by a contactor I turned by a shaft ,this

providing motor speed changes as The compensating field winding isin series with the armature circuit i and the auxiliary field is in shunt connection with the compensating field 35 winding by way of the shunt circuit C which includes theresistance I in series therewith, variable amounts of the resistance I being placed in the circuit by a contactor I turned by the shaft l. As previously explained, the contactors 3 and 8 move dependently in accordance with rotation of the shaft 4, the arrangement being so that as the resistance 2 is increased in the circuit I, the resistance 1 is decreased in the circuit 6, this preventing motor instability due to changes in the armature speed. However, it does not prevent unstable motor operation due to variations in the armature load.

In accordance with the invention, a second rheostat independent 01' the first is used, this including the resistance 0 in the circuit 0 parallel the resistance I and or which variable amounts are placed in the circuit by a contactor Ill. It is to be emphasized that the operation or the con-' taotor II is entirely independent of the operation of the contactor: I and ,l.

With the arrangement shown by the diagram,

' the motor speed is set by operation of the contactor I, this automatically and simultaneously adjusting the auxiliary field strength to control the armature speed droop characteristic in so far as the motor speed adjustment is concerned. Then, should the armature load suddenly vary as it does in rolling mill applications, the operator is free to adjust the contactor ll as required to increase or decrease the auxiliary field strength to control the armature speed droop characteristic resulting from armature load variations, this having been impossible before.

I claim: v w

A metal rolling mill motor having a shunt field for controlling its armature speed and an auxiliary field for controlling its armature speed droop characteristics, the motor having a compensating field with which the auxiliary field is inshunt circuit and the circuits of both the shunt and auxiliary fields including means i'or placing variable amounts of resistance in series with each with the amount placed in the one circuit dependent on the amount placed in the other so as to control the'armature speed while automatically controlling the armature speed droop characteristic resulting from armature speed variations, and the auxiliary field circuit also including means for placing variable amounts of resistance in parallel circuit with the resistance placed therein by the first named means so as to control the armature speed droop characteristic resulting from load variation, the

two means being respectively independent.

THORNTON A. WOOD. 

